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The task to control plasmas parameters is very important for many applications and research setups. Plasmas are characterized by a set of parameters as an electron density, an electron temperature, and gas, ion, "vibrational", "rotational" temperatures and so on. A most commonly used method for diagnostics of plasmas is a spectroscopy based on dependence of atom spectra on the plasma parameters. These methods [1] have a very significant advantage since they do not perturb the plasma state. The another important advantage is rather a large amount of information containing in the plasmas' spectrum. We are going to introduce the ICLS as a new plasma diagnostics technique because of its high sensitivity that could allow to perform measurements then other spectroscopic methods fail. We skip describing of the ICLS principles because the other part of this book doing it perfectly. Now we mention briefly the plan of our part. First of all, using of ICLS is required to know the errors of measurements of plasma parameters, we estimate some essential types of errors in Chapter 2. Investigation of non-equilibrium molecular plasmas are in Chapter 3. It is a plasma electric field that determines most of all the physical processes in plasmas. On the other hand, the problems of propagation of strong electromagnetic waves in plasma attract great interest in connection with the study of heating in confined plasmas [2]. The problems of wake-field excitation [3] are under presentday consideration. So, the problem of determination of the electric field inside plasma is one of the utmost importance. The atom levels affected by the electrical field are shifted due to the Stark effect, the value of this shift, being dependent of the field intensity and the constants of atom interaction with the electric field. If an a.c. field is present along with the level shifts, there are satellites of lines due to amplitude and frequency modulation of absorption. Thus, to determine the intensity of the electric field, it is required to measure the shifts and the intensity of satellites of lines. So, it is essential to have a method with high sensitivity, because the satellite intensities in low fields are very small, and with high spectral resolution, because the shifts of levels are small in low fields too. Plasma satellites arising due to Langmuir plasma waves are located near the forbidden lines at the distance of plasma frequency w = (4iie2Ne/me)11'2. For the case of fluctuations of electron density to registration of Langmuir satellites requires a method is needed which can register the whole spectrum of the atom by one shot . These very features are characteristic for the method of intracavity laser spectroscopy. Chapter 4 is concerned about the plasma field diagnostics by the ICLS. The interferometry methods of plasma diagnostics in the optical, infrared and millimeter bands of the electro-magnetic waves attract the researches' steady attention, as they assume simple interpretation of the obtained results, and are free from different modeling considerations, do not require any a priori data about the investigated plasma parameters. The application of these methods, however, in the most convenient in all respects optical range (high resolution, simplicity and reliability of the registration, etc.) is restricted by quite low sensitivity. This drawback is caused by the small refraction of the electromagnetic waves in the optical band and by the possibility of ising only double-slit interferometer, framing interference pictures with dark and light bands of the same width and that can not but hampers the registration of their small shifts. 167 168 The nature of selective losses is not essential for the ICLS so, it is easy to extend ICLS method into interferometry of plasmas, we deal with it in chapter 5. Here is what the present issue is about. We, with some small exceptions will refer to the works, done in our group. Though quite a number of researchers use the methods of intracavity laser spectroscopy, practically only our group is working at the implementing of this methods in plasma diagnostics.
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